1. Field of the Invention
The present invention relates to a frequency conversion apparatus which is effectively used for tuners and converters and the like.
2. Description of the Prior Art
In conventional frequency converters, especially one which is operated in switching mode by a local oscillator signal, the current flowing in the main terminals of component transistors suddenly increases by the injection of the local oscillator signal. Therefore, the difference in the operating current is considerable depending on the presence of the local oscillator signal to be injected. Accordingly, it was necessary to operate the frequency converter with a constant current.
Consequently, an amplifier is directly connected to the mixer section to control the increase in the current and this amplifier is used as an amplifier for the high frequency input signal. Such configurations are shown in "GaAs FET up converter for TV tuner" by U. ABLASSMEIER et al, IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. ED-27, No. 6, June 1980.
With such configurations, however, the amplifier is used only for amplification of the high frequency input signal. On the other hand, because the amplifier and the mixer section are directly connected, it was necessary to design the device while paying attention to the impedance matching therebetween.